People who are found guilty of spamming the search engine, many of them don’t even realize that why they spamming. Following are some of the methods that help them in improving ranks but actually it cause them in descending in their website ranking.
Some important points to avoid:

1- Use text with the same color as that of background color in order to hide text.
2- A common mistake is repeating keywords in meta tags again and again. In my discussion with some of the gurus in this business they suggest that no words should be appear in the Meta description and in Meta keywords more than three times.
3- Title is one of the most important factors of on page SEO. It must be appealing and attractive. Title like “SEO Services, SEO Services, SEO Services…etc” is consider as spam and also found very less attraction from the people.
4- Avoid overloading page with keywords. Content of the page must not abuse reader. This technique is easy to spot, and it is clearly spam.

5- Replace the indexed page content with another page.
Unrelated and misleading words on your page or in Meta description in order to attract visitors how are searching for that word. Like use of word “Michel Jackson” on a site having business of furniture.

6-Create such page that restricts the users to go back to the SERP (search engine result page).
7- Avoid the submission of same page to the search engines again and again.
8- Avoid the use of transparent gif. This is done by assigning them with same alt text.

Lat but not the least Don’t use multiple versions of title tag. They may help for some time but easily caught by the search engine.
This is just starting hints. There are some more advanced spamming techniques that must be avoided, but I hope you get a good idea how to remain safe for being called spammer. Try to follow these rules as these rules must be your model for what to do and what not to.

Another bad one is linking just to the front page to much and not letting your readers inside. I have been told it is better to deep link and get the searcher to his point of interest. I have a site that is just a catalog but give all the content on pre sites that are static like hubpages and this works.

The article describes some but the most important black hat techniques to avoid by penalizing by Google or any of the other Search Engines. Another thing which is not clearly mentioned in the article is to avoid excess use of keywords that is keyword stuffing.

I have seen people even hiding keywords behind some layers... hahah. There are so many such not black rather dirty and useless techniques taking Search Engine as fools, which they are not. Over stuffing of keywords by any such means is the most common mistake. There is a phrase "keyword density" and it has to be maintained religiously.